1. Field of the Invention
The present invention relates to an image forming material and an image forming method, particularly, the present invention relates to an image forming material and a method of forming an image therewith by a dry process in which a photopolymerizable composition is used.
2. Description of the Prior Art
Heretofore, as photoresist materials for producing printed circuits, often solution development type recording materials such as a light-sensitive solution in which a dichromate is used in combination with glue, polyvinyl alcohol and the like, a light-sensitive solution mainly composed of polyvinyl cinnamate and a sensitizer and a light-sensitive solution mainly composed of natural rubber or synthetic rubber and a crosslinking agent, etc., have been used.
Further, a recording material is known in which a light-sensitive layer is interposed between two plastic films. In this case, one of the plastic films is peeled off to expose the light-sensitive layer and the recording material is laminated onto the metal which is to form the printed circuit, typically copper, in such a manner that the light-sensitive layer comes in contact with the area which the printed circuit is to be formed. The recording material thus laminated is imagewise exposed to light through the other plastic film and, after removal of the other plastic film, is developed with a developing solution such as an organic solvent, an alkali aqueous solution or the like. The areas where the light-sensitive layer has been cured by irradiation remain on the copper plate, whereas the areas where the light-sensitive layer has not been cured are dissolved in the developing solution and removed. In this way, the desired resist pattern for the printed circuit is produced.
However, the above described solution development type of recording materials are complicated in use in that a developing solution must be used and, furthermore, the use of a developing solution is not desired in that it often leads to environmental pollution.
Recently, in place of such solution development type recording materials, recording materials have been proposed in which dry development is possible. For example, U.S. Pat. Nos. 2,951,758 and 3,060,023 describe a method of forming an image in which the difference in adhesion strength to the support between exposed areas and unexposed areas at a heating temperature of about 40.degree. to 220.degree. C is utilized. In accordance with this method, a layer of a photopolymerizable composition mainly composed of a polymer (as a binder), an unsaturated monomer and an initiator for photopolymerization is provided on a support such as a plastic film, a metal plate, paper and the like, and a thin transparent film is provided on the photopolymerizable composition layer. Imagewise exposure is applied from above the thin transparent film, and then the thin transparent film is peeled off, whereby exposed areas and unexposed areas of the light-sensitive layer on the support of transparent film are selectively removed to give negative and positive images (or positive and negative images) on the support and transparent film, respectively.
In the case of using such a recording material, development using a liquid is omitted, and a resist pattern is formed merely by peeling off the transparent film. A great deal of labor is saved in producing printed circuits using this method.
In accordance with this method, since the combination of (a) an unsaturated monomer, (b) a binder, and (c) a photopolymerization initiator determines the sensitivity, the characteristics of the images obtained and the like, various combinations have been proposed. However, no light-sensitive composition having completely satisfactory properties has been discovered until the present invention.